Objectives

• Define ‘Moh’s Hardness Scale’ and discuss its importance in abrasion.
• Identify factors affecting the rate and efficiency of abrasion.
• Define and explain the concepts of abrasion, finishing, polishing, and cleaning.
• List and describe materials used in abrasion.
• Describe various delivery designs of abrasives.
• Discuss safety and infection control precautions when using abrasives.
• Relate patient instructions for preventing and removing stain from tooth surfaces and restorations.

Definitions

• Abrasive: A material composed of hard and sharp particles that can cut or scratch softer materials when rubbed across their surface.

• Finishing: A procedure that reduces excess restorative material to develop appropriate occlusion and contour. It removes surface blemishes, produces a smooth surface, and is typically achieved with rotary cutting instruments. Care is required to avoid damaging adjacent tooth structures.

• Polishing: A procedure that generates a shiny, smooth surface by eliminating fine scratches and surface imperfections using mild abrasives (pastes or compounds). Requires materials with a Moh's hardness of only 1-2 units above the material being polished, and may need to be repeated periodically during the lifespan of restorations.

• Cleaning: The removal of soft deposits from teeth and restorations. It may involve abrasives and chemical cleansing products, requiring materials with Mohs’ hardness no greater than that of the substrate.

Finishing and Polishing Procedures

• A finished and polished restoration should be smooth and continuous, flush with the tooth surface.
• Benefits of proper finishing and polishing:
  • Decreased biofilm retention.
  • Increased resistance to tarnish and corrosion.
  • Increased longevity of restorations.
  • Decreased attrition of natural tooth surfaces during chewing.
  • Improved esthetics.
  • Enhanced health of surrounding tissue.
• Before finishing or polishing, check for flash (extra material) and proper margination (removing excess material to align restorations with tooth structure).

Mohs' Hardness Scale

• Ranks materials by relative abrasion resistance:
  • Diamond: 10 (highest resistance)
  • Enamel: 5
  • Dentin: 4
  • Cementum: 2-3

Factors Affecting Abrasion

• Size, irregularity, and hardness of particles.
• Number of particles contacting the abraded surface.
• Speed and pressure applied by the abrasive.

Delivery Designs of Abrasives

• Paste: Prophy paste/toothpaste.
• Loose powder: Classified by grit or particle size.
• Bonded: Used with rotary instruments; particles uniformly incorporated within a formed shape.
• Coated: Particles secured to one side of strips or discs.

Materials Used in Abrasion

• Diamond: Hardest substance; bonded for cutting or polishing.
• Carbide Finishing Burs: Varied shapes for finer finishes.
• Silicon Carbide: Synthetic abrasive (Mohs’ 9-10).
• Aluminum Oxide: Used in air abrasion and smoothing enamel.
• Sand: Natural abrasive (Mohs’ 7).
• Silicon Dioxide: Mohs’ 6-7; often used in prophy paste.
• Pumice: Volcanic silica; used in polishing.
• Rouge: Iron oxide (Mohs’ 5-6) for precious metal polishing.
• Tin Oxide: Final polishing agent for enamel/restorations.
• Calcium Carbonate: Chalk (Mohs’ 3) for teeth and metal polishing.

Laboratory Finishing and Polishing Techniques

• Polishing devices include:
  • Rag Wheel: Made of muslin, adds polishing agent for buffing.
  • Felt Cones/Wheels: Felt devices that smooth with abrasive agents added.

Safety and Infection Control

• Aerosols created by rotary devices can transmit diseases if PPE is not used. Potential health risks include:
  • Silica particles and mercury vapors.
• Personal Protective Equipment (PPE):
  • Lab coat
  • Mask
  • Safety glasses
  • Shield (as needed)

Summary Questions

1. What steps does a clinician take during polishing, cleaning, and finishing?
2. What is the Mohs’ Hardness Scale and its significance?
3. What are the benefits of a correctly finished and polished restoration?
4. Which materials are particularly susceptible to staining? How to evaluate them?
5. What PPE should be worn during finishing and polishing in the lab?